Various types of laser machining apparatuses are known. For example, Japanese Patent Application Laid-Open Publication No. 5-8079 (see page 2, FIGS. 1 and 2) discloses a conventional laser beam machining apparatus that transmits a laser beam stably for long time and can weld and cut a subject to be machined with high accuracy. This laser beam machining apparatus includes a laser oscillator, a laser robot, an optical duct, and a machining gas supply unit. The laser oscillator has a beam transmission line including a laser outgoing port of an airtight mechanism. The laser robot has an articulated configuration which can emit a laser beam to an arbitrary position of the subject to be machined. The optical duct guides the laser beam so that an optical axis of the laser beam between the laser oscillator and the laser robot does not shift. The machining gas supply unit detects pressure in the optical duct and supplies a predetermined machining gas into the optical duct so that the pressure in the optical duct becomes higher than external pressure. Such a configuration prevents fume and dust generated at the time of the laser beam machining from entering the optical duct through a tip of the laser robot.
Japanese Patent Application Laid-Open Publication No. 6-17120 (see pages 2 to 3, FIG. 1) discloses a laser annealing apparatus capable of controlling intensity of a laser beam accurately according to a condition where a subject to be machined undergoes a laser annealing process. The laser annealing apparatus has such a configuration that the laser oscillator and a chamber in which the subject to be machined and to undergo the laser annealing process is arranged are connected by the optical duct. The laser annealing apparatus adjusts the intensity of the laser beam emitted to the subject to be machined in the chamber based on purge gas which does not absorb the laser beam transmitting through the optical duct, and concentration of control gas having predetermined absorptance with respect to the laser beam. The optical duct, therefore, has a detecting sensor which detects the concentration of the control gas in the optical duct, and a quantity of the control gas to be supplied into the optical duct is controlled based on a signal obtained in such a manner that the detecting sensor detects the concentration of the control gas.
In the conventional laser beam machining apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 5-8079, however, air might enter the optical duct. One of causes that the air enters the optical duct is a configuration of the optical duct. As shown in FIG. 1 of this publication, for example, the optical duct which connects the laser oscillator and the laser robot does not have a linear form, and the optical path is bent at a plurality of portions. Such an optical duct is normally constituted so that bellows or the like connects a plurality of pipes. The laser beam machining apparatus of the first prior art has the laser robot in which a position to which the laser beam is emitted can be moved so that the laser beam can be emitted to an arbitrary position of a subject to be machined. In the laser beam machining apparatus having such a configuration, for example, a bellows section composing a part of the optical duct occasionally moves according to a changing operation of the emitting position of the laser robot which is performed in order to change the laser beam emitting position, or when the laser beam machining is stopped, pressure in the optical duct temporarily drops. As a result, for example, outside air enters the optical duct through joints of the pipes composing the optical duct or joints between the pipes and the bellows.
Another cause that the air might enter the optical duct is machining gas to be supplied into the optical duct, and this is caused by using air sucked from a compressor into the optical duct as the machining gas.
If the air enters the optical duct, when thinner, paint, or the like is used in a vicinity of the optical duct, impure gas such as laser beam absorbing gas (thinner, trichloroethylene, acrylic combustion gas, fluorocarbon gas, SF5, organic compound, and the like) enters the optical duct. The impure gas causes power distribution of the laser beam and increase in attenuation of the laser beam, and as a result, characteristics of the laser beam are deteriorated, and thus machining ability of the laser beam machining apparatus is deteriorated.
When anomalous output of the laser beam occurs, a defect in the laser oscillator is firstly regarded as a cause of the fault. After various factors which cause the fault in the output of the laser beam are eliminated, it is frequently found that the intrusion of the impure gas into the optical duct is the cause of the anomalous output of the laser beam. That is to say, the impure gas in the optical duct cannot be specified as the cause of the anomalous output of the laser beam in the early stage of the checkup of the causes. During the checkup of the causes, therefore, the machining cannot be carried out by the laser beam machining apparatus, and thus the impure gas is also a cause for deteriorating working efficiency.
In the laser annealing apparatus disclosed in Japanese Patent Application Laid-Open Publication No. 6-17120, the detecting sensor which detects the control gas is provided in the optical duct, but the detecting sensor detects the concentration of the control gas which controls the output of the laser beam and does not detect the impure gas. That is to say, even if the impure gas such as the laser absorbing gas enters the optical duct, the detecting sensor cannot detect the intrusion of the impure gas.
It is an object of the present invention to solve at least the problems in the conventional technology.